Our feline friends are constantly being studied. Their behavior fascinates us and keeps us guessing why they act the way they do. Here is some research I found around the web about why cats bite us.
Cats will bite out of playfulness or aggression. When a cat is content, a cat will playfully nip, which is a type of bite which is weak and harmless. A common misunderstanding about the motivation behind a cat's bite is that it is a form of affection. People most likely assume this because a cat will sometimes bite suddenly while it is being petted. A petting-induced bite is not a form of affection, but rather a mildly aggressive signal to inform the human to stop petting. While this behavior may seem unexpected to humans, a cat will usually give other subtle indications, such as "tail-lashing or thumping, skin rippling, growling, cessation of purring, ear flicking or rotation sideways, or shifting of body position" to announce that it does not wish to be petted.
Cats also have sensors in their teeth, and biting could indicate curiosity, similar to a human baby's exploration of their environment by inserting objects in their mouths.
Interesting stuff. Why does your cat bite?
cats cats biting